1. Field of the Invention
The present invention relates to a lens-fitted photo film unit provided with a stop-changing mechanism, and further relates to a stop-changing device used for a photographic camera, an electronic still camera, a lens-fitted photo film unit and so forth.
2. Description of the Related Art
Various kinds of lens-fitted photo film units are manufactured and sold. Such a lens-fitted photo film unit includes a simple photographing mechanism and is loaded with a photo film at the time of manufacture thereof. The whole of the lens-fitted photo film unit is formed so as to have a flat shape in order to improve portability and design. However, it is necessary to secure a focal length of about 30 mm, which is fit for snapshot photographing. Thus, shortening a light-shielding box is impossible. For this reason, a protrusion is provided around a taking lens to contain peripheral parts of the taking lens inside the protrusion.
The lens-fitted photo film unit employs a shutter mechanism of a kicking type in which a single shutter blade is kicked to rotate. The protrusion has a size to be capable of containing the shutter blade and a rotational space thereof.
When the conventional lens-fitted photo film unit performs flash photographing in a dark room and in the night-time, a main subject existing within a flash-light reaching distance may be photographed under adequate exposure. In contrast, the background beyond the flash-light reaching distance is darkly photographed because luminosity to be received is small. In order to solve this, the lens-fitted photo film unit disclosed in Japanese Patent laid-Open Publication No. 10-333287 is provided with a stop-changing mechanism for rotating a stop-changing plate formed with a smaller stop and for selectively placing the stop-changing plate at a photographic optical axis behind a taking lens. When flash photographing is performed, a stop is enlarged to increase marginal luminosity to be received.
Meanwhile, some of the various lens-fitted photo film units have a taking lens constituted of a front lens and a rear lens for the purpose of improving photographic image quality. Between the front lens and the rear lens, a stop is disposed.
When the stop-changing mechanism is built in the lens-fitted photo film unit using the stop disposed between the front and rear lenses, a space for moving the stop-changing plate is also necessary in the protrusion. If a rotational direction of the shutter blade is different from that of the stop-changing plate, the protrusion should be enlarged. In this case, portability and design are greatly constrained.
Japanese Patent Laid-Open Publication Nos. 2001-133832 and 2001-21940 disclose the lens-fitted photo film unit including the stop-changing mechanism, which changes the exposure by selectively placing the stop-changing plate at a photographic optical axis behind the taking lens.
The lens-fitted photo film unit disclosed in the former publication has a built-in photometry mechanism for automatically performing photometry in response to shutter release. Before opening and closing the shutter blade, the stop is changed in accordance with subject brightness obtained by the photometry mechanism.
Meanwhile, the lens-fitted photo film unit disclosed in the latter publication is provided with a flash switch selectively set to one of three modes of a diurnal photography mode, a diurnal synchronized-flash photography mode, and an indoor/nocturnal photography mode. Under the diurnal photography mode, a smaller stop is set to the photographic optical axis and the flashlight is prohibited. Under the diurnal synchronized-flash photography mode, the smaller stop is set to the photographic optical axis and the flashlight is emitted. Under the indoor/nocturnal photography mode, the smaller stop is evacuated from the optical axis to use a fixed larger stop and the flashlight is emitted. In this way, a flash device and the stop-changing mechanism are controlled in association with the flash switch set to the respective mode positions.
By the way, nowadays, the taking lens having a two-group two-lens structure is mainly used in view of advantageous relative to aberration correction. As to a type having this kind of the taking lens, for instance, Japanese Patent Laid-Open Publication No. 2002-250956 discloses a stop-changing device for inserting a smaller-stop plate between adjacent lenses.
The stop-changing device is provided with a front lens, a flare stopper, a spacer and a rear lens, which are arranged in order from a subject side, and the spacer constituting a fixed-stop plate is provided with a cut potion for securing a passage of the smaller-stop plate. This smaller-stop plate is inserted into a thickness of the spacer. In order to prevent an interference relative to a lens surface at the time of insertion, a circular rib is protrusively provided on the front of the rear lens. The smaller-stop plate is held by the rib and the back of the flare stopper in a direction of the photographic optical axis.
However, since the circular rib having a certain length is necessary on the front of the rear lens to hold the smaller-stop plate in the optical-axis direction, the taking lens is prevented from having a preferable formation. Further, since the smaller-stop plate moves within the thickness of the spacer in the optical-axis direction, stable high-image quality is hardly obtained.
In view of the foregoing, it is a primary object of the present invention to prevent a peripheral protrusion of a taking lens from enlarging in a lens-fitted photo film unit, which includes a stop-changing mechanism and a stop to be placed between lenses constituting the taking lens.
It is a second object of the present invention to provide a stop-changing device in which formation of lenses is free from restraint and a stop may be stably changed.
In order to achieve the above and other objects, the lens-fitted photo film unit according to the present invention comprises a shutter blade, a rotational center of which coincides with or approximates to a rotational center of a stop-changing plate. Further, a rotational direction of the shutter blade from a closed position to an open position is set so as to be identical with a rotational direction of the stop-changing plate directing from a smaller-stop position to a larger-stop position.
In a preferred embodiment, a changeover ring to be rotated in accordance with a stop changing operation is disposed around a lens barrel. In association with this changeover ring, the stop-changing plate is moved between the smaller-stop position and the larger-stop position. It is possible to utilize the rotation of the changeover ring for the purpose of changing a shutter speed.
In the lens-fitted photo film unit according to the present invention, the rotational centers of the shutter blade and the stop-changing plate are approximated to each other and the rotational directions thereof are identical. Thus, the shutter blade and the stop-changing plate can share a rotational space thereof. Owing to this, a protrusion around a taking lens has a similar size in comparison with that of a conventional lens-fitted photo film unit so that portability and design may be maintained. Further, since a stop and a shutter speed are changed by the change over ring rotating around the lens barrel, the protrusion may be downsized.
The stop-changing device according to the present invention comprises a horseshoe-shaped spacer and a stop plate, which are disposed between two lenses constituting a taking lens. The stop plate has a fixed stop and the spacer has an opening equal to or larger than the fixed stop. Thickness of the spacer and the stop plate maintains an interval of the lenses at constant. The spacer is formed with a concave portion hollowing stepwise. A stop-changing plate having a smaller stop enters the concave portion and evacuates therefrom to change the stop. The stop-changing plate is moved within a depth of the concave portion. A surface of the concave portion prevents the stop-changing plate from waggling in an optical-axis direction.
In the stop-changing device, the stop-changing plate is prevented to the utmost from contacting the lens. Further, the stop-changing plate hardly waggles in the optical-axis direction so that image quality may be prevented from deteriorating.